Help! Is this a mixed model ANCOVA?

Hi, I could really use some help.

I am conducting a study looking at the different growth rate of two species of trees (100 of each) randomly places in a 10km^2 urban area. Their average growth rate is recorded. In addition to the species, the locals water the individual plants (in addition to rainwater) and it is recorded. Therefore I am going to use ANCOVA looking at the if there is a difference in growth rate between the two species, accounting for the effect of water (covariate). What I am confused about is whether water is a random or fixed effect? Can someone please help me??


Active Member
im voting for fixed. That would be standard ANCOVA model anyway. If you made the effect of water random you would have a 'random slope' wouldn't you? I don't think that is productive in this case,

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